(1) Field of the Invention
The invention relates to turbomachinery. More particularly, the invention relates to gas turbine engines having compressor bleeds.
(2) Description of the Related Art
Axial flow gas turbine engines include a compressor, a combustor and a turbine. A core flowpath for medium gases extends through these portions of the engine. During operation, the gases are pressurized in the compressor and fuel is added in the combustor. The fuel is burned to add energy to the pressurized gases. The hot, pressurized gases are expanded through the turbine to provide the work of hot, high pressure gases for subsequent use. Common gas turbine engine configurations divide the combustor and turbine into high and low speed/pressure sections whose blades are mounted on respective high and low speed spools. Additionally, a broad spectrum of turbine engines provide a bypass wherein the turbine (typically the low speed section) drives a fan which, in turn, propels gas along a flowpath bypassing the core flowpath.
Under certain conditions, air is bled from a compressor section for one or more purposes. The air may be bled for use such as in cooling. Alternatively, however, the air may be bled to reduce the load on the associated turbine section under certain operating conditions. An exemplary such operating condition is a transient startup condition. Such load-reducing bleeds may be controlled by a bleed valve. U.S. Pat. No. 6,092,987 of Honda et al., the disclosure which is incorporated by reference herein, discloses a stator assembly having a valve ring moveable between first and second conditions in which the ring respectively blocks and opens communication through bleed openings in a stator housing. Shifting between the first and second conditions is via a combination of rotation and longitudinal translation so as to provide a mechanical advantage. Nevertheless, there remains room for further improvement in bleed valve technology.